It is known that the comfort of a shoe is linked not only to its anatomically fitting properties but also to the capacity to dissipate outward the water vapor that forms inside the shoe due to sweating.
For this reason, waterproof shoes with an upper coupled to a lining that is laminated with a waterproof and vapor-permeable membrane have now been known for years.
The expression “waterproof and vapor-permeable” generally references the characteristic of tightness to water in the liquid state combined with permeability to water vapor.
The portion of the foot that notoriously has the greatest perspiration effect is the sole, and the sweat that it generates saturates the air with moisture and mostly condenses, stagnating on the footbed.
Only a marginal fraction of the moisture produced by sweating is diffused to the sides of the upper and exits from them if they are vapor-permeable.
In order to allow easy dissipation of the sweat that tends to accumulate in the region of the sole, shoes are currently known which have different types of rubber soles that are impermeable to water in the liquid state and are permeable to water vapor and are obtained by using a vapor-permeable and waterproof membrane, which is sealed to the body of the sole so as to cover through openings thereof.
The production method commonly known as “AGO lasting” has long been known in the shoe manufacturing field and provides, with an operation known as lasting, for pulling the upper shoe assembly onto the last, folding its lower edges, known as lasting margins, under an insole, to which they are glued perimetrically, so as to interpose themselves partially between said insole and the sole that will be assembled thereon.
Assembling the sole consists in joining the sole to the upper portion of the shoe, by gluing or by direct injection in a mold.
So-called “AGO lasting” construction is generally used for shoes of the type generally classified as classic or elegant.
Stretching the upper and the lining on the last in fact allows to make them adhere thereto precisely, achieving effective formation.
The assembly insole is made of a flexible material that however is structured enough to not undergo deformation due to the traction applied thereto by the lasting margins glued onto it during lasting.
Currently it is known that even when the upper shoe assembly has a waterproof and vapor-permeable membrane, inserted between the outer layer of the upper and the inner lining without additional refinements, then there is a substantially total lack of waterproofing.
The “AGO lasting” construction, in the way it is currently performed, in fact allows penetration of water toward the inside of the shoe through the outer layer of the upper and through the insole.
A need that is particularly felt in the manufacture of shoes with a waterproof and vapor-permeable membrane, in the upper shoe assembly, consists in achieving an effective seal of the joining regions between the insole, the lining with membrane, the outer layer of the upper and sole, in order to avoid even the slightest infiltration of water from outside.
It is in fact particularly difficult to seal the sole to said membrane, since in so-called “AGO lasting” construction the bottom of the shoe is not smooth and flat, as occurs for example in the case of “Strobel” construction, in which the edges of the insole are sewn to the edges of the upper or of the lining laminated with the membrane, but the lasting margins of the upper are superimposed on the assembly insole, creating irregularities along its perimeter.
In particular, the creases produced as a consequence of the assembly of the toe and heel of the upper onto the assembly insole constitute actual channels for water infiltration.
However, it is not possible to remove these protrusions by means of the common operation of roughing the upper with steel brushes, since this operation might damage the waterproof and vapor-permeable membrane inserted between the upper and the lining.
Accordingly, as described for example in patent application WO 9316612, shoes have now been studied for years which have a waterproof and vapor-permeable insole which comprises a waterproof and vapor-permeable membrane with which the lasting margins of a lining with a waterproof and vapor-permeable membrane are associated by means of a first lasting operation.
The joining region between the lining with the membrane and the insole is sealed by means of a waterproof sealing tape.
The lasting margins of the outer layer of the upper are then associated, by means of a second lasting operation, with the waterproof and vapor-permeable insole.
The embodiment is not free from aspects that can be improved, since the water absorbed by the outer layer of the upper and wicked inside it can stagnate below the waterproof insole.
Moreover, this construction has an additional drawback if a sole provided with openings is used, since water might enter through said openings and wet the lasting margins of the upper, impregnating it and thus rising toward the foot insertion region.
Moreover, the use of a waterproof and vapor-permeable membrane that covers the entire surface of the insole, if the vapor-permeable surface of the sole does not extend over its entire longitudinal direction, is useless and very expensive.
An alternative to the use of a waterproof and vapor-permeable insole is described in U.S. Pat. No. 5,426,869, in which a waterproof layer acting as a gasket is provided by a non-woven polyester fabric that is uniformly coated on one of its faces with a layer of adhesive based on polycaprolactone. This waterproof gasket is used to fill the area comprised transversely between the lasting margins of the lining or upper, if they are waterproof and vapor-permeable, and constitutes a waterproof layer between the insole and the sole.
Since the gasket is made of waterproof and non-vapor-permeable material, this construction is unsuitable with a rubber sole rendered impermeable to water in the liquid state and permeable to water vapor by means of regions that are open or perforated and are covered and sealed with a waterproof and vapor-permeable membrane.
Moreover, if the gasket is pierced at the vapor-permeable area of the sole, in order to allow the outflow of the water vapor generated by sweating, the lasting margins of the outer layer of the upper would wick, toward the inside of the shoe, the water, which would migrate onto the insole indeed through the holes in the gasket.
An alternative to these solutions is to use a lining with a waterproof and vapor-permeable membrane that is closed like a sock, so as to wrap around the foot completely.
An insole is applied to the bottom of the sock and the lasting margins of the outer layer of the upper are folded and glued onto it perimetrically.
The sock-like lining comprises an opening for the foot and is generally formed by two lateral portions and a lower portion, the connection of which is provided by means of zigzag and/or Strobel seams and sealed by means of waterproof sealant tape.
It is well-known that this production method is very complicated and delicate.
Moreover, precise shaping of the sock closed by means of seams and not by lasting on a last is difficult to achieve, both due to difficulty in preparing the various components that must be cut and sewn with accurate precision and due to difficulty in achieving correct tension, without creases, between the upper and the lining.
Indeed, due to the fact that during the sewing of the lining the last is not used, said lining tends to wrinkle during the lasting of the upper, contrary to what instead occurs when one uses “AGO lasting” construction, which allows to obtain an upper and a lining that are correctly formed, stretched and smooth.